How many different type of scripts are there in the world?

There are at least 6000 languages currently spoken, but not all of them have a writing system and some of them use modified forms of existing writing systems. As for types, there are alphabets (e.g. English, Georgian, Cyrillic), syllabaries (e.g. Japanese kana, Native American languages such as Ojibwe and Cree, Yi), syllabic alphabets (e.g. Bengali, Hmong, Thai), abjads (e.g. Arabic, Hebrew), and semanto-phonetic scripts (e.g. Chinese, Japanese kanji, Egyptian hieroglyphs). There may be other, still unknown types hidden in undeciphered scripts, but for now these five are clearly identified.

Information on scripts can be found here:

http://omniglot.com/

http://en.wikipedia.org/wiki/List_of_writing_systems